1. Field of the Invention
The present invention related to impurity-removing apparatus for effectively removing solid, chemical impurity substances besides gaseous impurity substances in the air, and more particularly concerns impurity-removing apparatus suitable for use in the semiconductor fabrication process.
2. Related Art
If there are impurities, such as dust particles in the atmosphere in the manufacturing process of semiconductor devices, such as LSIs, they cause variation or deterioration in the electrical characteristics of the semiconductor devices. For this reason, the filtered air is used for the atmospheric air in the semiconductor fabrication process to improve the reliability of the electrical characteristics of the semiconductor devices and to prevent a decrease in production yield in the fabrication process. Or, the exiting air from the clean room in the semiconductor fabrication process is cleaned and returned to the clean room.
Examples of the impurity-removing apparatus for cleaning the air are disclosed in Japanese Patent Laid-Open Publication Nos. Hei 7-60044 and 2000-33221.
According to those impurity-removing apparatuses, by using wet-type removing means for atomizing a liquid to capture gaseous impurity substances, they can be removed from at a relatively high removal rate.
It ought to be noted that in addition to gaseous impurities, the air contains dust particles other than chemical substances and particles of chemical substances. Being effective in collecting dust particles other than chemical substances, the dry filter may be incorporated in the prior-art impurity-removing apparatuses mentioned above to effectively remove gaseous impurity substances dust particles other than chemical substances.
However, with a dry filer mounted in the conventional impurity-removing apparatus, it is impossible to effectively remove particles of chemical contents, such as Na or K. Therefore, there has been demand for impurity-removing apparatus capable of effectively removing particles of chemical substances.
To solve the above problem, the present invention adopts the following configurations.
According to one aspect of impurity-removing apparatus of the present invention, basically comprises a housing defining a flow passage guiding the air to be treated; a first filter, located in the flow passage, for removing solid particles contained in the air; first cooling means, located downstream from the first filter in the flow passage, for cooling the air to be treated below a dew-point temperature;
a wet-type removing mechanism for capturing gaseous substances in the air cooled below a dew-point temperature; second cooling means, located downstream from the wet-type removing mechanism in the flow passage, for cooling the air to not higher than its dew-point temperature to condense an atomized liquid containing the gaseous substances remaining in the air; and a second filter located downstream from the second cooling means in the flow passage and using a material denser than that of the first filter.
The above-mentioned wet-type removing mechanism includes first capturing-liquid atomizing means for atomizing a capturing liquid for capturing gaseous substances in the air cooled below a dew-point temperature, the first atomizing means having a plurality of atomizing nozzle ports mutually spaced apart and facing each other in the direction of the flow passage; first and second condensing and capturing means for capturing an atomized liquid containing the gaseous substances, the first and second condensing and capturing means being located across the first atomizing means and spaced apart from each other, the first capturing means upstream from and the second capturing means downstream from the first atomizing means.
In another aspect of the impurity-removing apparatus the present invention, by realizing the above-mentioned configuration, more specifically, only after making a combination of the wet-type removing mechanism, the first and second filters, and the first and second cooling means, has it become possible to remove not only dust and gaseous substances and also particles of chemical substances at a high removal rate.
Regarding to the improved removal rate of particles of chemical substances, it is considered that the good effects are considered as resulting from the way in which the first capturing-liquid atomizing means sprays the capturing liquid in opposite directions from the ports spaced apart from each other and facing each other in the direction of the flow passage.
In yet another aspect, it is possible for the first and second atomizing means to spray the same or mutually different capturing liquids.
The first atomizing means may spray a capturing liquid, which is alkaline or acid, to neutralize an aqueous solution of gaseous impurity substances to be removed, which is acid or alkaline, while the second atomizing means may spray a rinsing water, such as demineralized water.
Or, the first atomizing means may spray a capturing liquid, which is alkaline or acid and the second atomizing means may spray a capturing liquid, which is acid or alkaline, in other words, opposite in character to the liquid sprayed from the first atomizing means.
Further, the first atomizing means may spray industrial water, well water or city water, which is relatively cheap, and the second atomizing means may spray more expensive demineralized water, thereby saving running cost of the impurity-removing apparatus.
In an additional aspect, as the condensing and capturing means, well-known eliminators may be used, which are subject to relatively smaller pressure loss.
In a further aspect, the average particle size or the average diameter of the capturing liquid atomized by each of the atomizing means is desirably 10 xcexcm to 100 xcexcm.
In another aspect, as cooling means, a well-known condenser coil may be used.
In a still another aspect, from a viewpoint of running-cost saving, the capturing liquid sprayed from the atomizing means is preferably recirculated between the atomizing means and the condensing and capturing means.